The present invention relates to a new and improved construction of gas-blast switch.
Generally speaking, the gas-blast switch of the present development is of the type comprising both a fixed contact element and a movable contact element. A blast nozzle is operatively associated with one of the contact elements, the blast nozzle having an inlet which can be connected with the outlet of a pump chamber. This pump chamber contains an extinguishing gas and is pressurized during the course of a cutoff stroke of the gas-blast switch. The narrowest location or throat of the blast nozzle is arranged downstream of the end of the related contact element. Between the inlet of the blast nozzle and the pump chamber there is provided a valve arrangement. This valve arrangement is pre-biased in the closing direction, responds to excess pressure conditions prevailing in the pump chamber and opens in the direction of the inlet.
Such type gas-blast switches are known, for instance, from German Pat. No. 2,316,009, corresponding essentially to Swiss Pat. No. 573,171, or from German Patent Publication No. 2,411,897. With the heretofore known gas-blast switches of this type the valve arrangement merely consists of a pre-biased check valve. This check valve is assigned the task of suppressing the connection between the pump chamber and the inlet chamber of the blast nozzle as soon as the pressure, emanating from the extinguishing gas in the blast nozzle which is heated by the arc, exceeds the momentary pressure prevailing in the pump chamber, to thereby prevent any return flow of this heated gas back to the pump chamber. With the state-of-the-art gas-blast switches the blast nozzle itself therefore must be capable of withstanding such pressure surge, and those heated gases located between the throat of the blast nozzle and the end of the related contact element appreciably render more difficult the outflow through the nozzle throat. Therefore, with the heretofore known gas-blast switches there is formed a thermal and a pressure bridge or dam at the inlet chamber of the blast nozzle, which has the result that the blast nozzle is exposed to burn-off phenomenon and appreciable mechanical loads, and therefore must be appropriately dimensioned and designed.